A patient who is suffering from atrial fibrillation can experience a ventricular rate (bpm) that is higher than normal for that patient. This can result in adverse effects of left ventricular function. Some examples of these effects are diminished preload and contractility of the chambers due to shorter filling intervals. Atrial fibrillation (AF) is recognized as the most common clinically significant cardiac arrhythmia. Current data estimated that 2.3 million Americans have AF. Because the prevalence of AF increases with age and because of the aging population, the number of AF patients is estimated to increase 2.5-fold during the next 50 years.
Currently, there are two broad strategic treatment options for AF: rhythm control and rate control. Although rhythm control (restoring and maintaining the sinus rate) is thought to be ideal, it cannot be achieved or maintained in a large number of patients, rendering rate control (controlling ventricular rate while AF continues) the only realistic long-term solution in a majority of patients. Recent clinical trials have demonstrated that rate control is at least as good as rhythm control for most patients with AF. Thus, rate control can be considered a “primary approach” in treating these AF patients.
The strategy of rate control during AF essentially deals with efforts to utilize and adjust the filtering properties of the atrioventricular node (AVN) because the AVN is the only normal structure responsible for the conduction of atrial impulses to the ventricles. Drug therapy (calcium channel antagonists, β-blockers, and digitalis) is the most common approach in rate control. However, drug therapy is not effective in some patients and may not be well tolerated in others because of side effects. These various drugs have been used to slow down the heart rate by lengthening the refractory period of the AV node. Although this therapy sounds reasonable, one side effect is that in many cases the patient is required to take combinations of drugs to control the ventricular rate, and another is that patients who have intermittent episodes of atrial fibrillation can experience excessive bradycardia due to inappropriate drug induced inhibitions of the AV node when the atrium is in sinus rhythm.
AVN modification can be used to control the ventricular rate. Because of the limited success rate and high probability of complete AV block, it is currently recommended only when AVN ablation with pacemaker implantation is intended. The latter option results in a lifelong pacemaker dependency. In addition, there are hemodynamic drawbacks because of the retrograde ventricular contraction. Recently, lesions encircling rather than destroying the AVN were shown to result in acceptable junctional escape rhythm. However, this technique needs further refinements and verification.
Recently, a novel strategy, selective AVN vagal stimulation (AVN-VS), has emerged for rate control during AF. It has been demonstrated that AVN-VS could be used to achieve desired predetermined ventricular rate slowing with improved hemodynamics in acute experiments. Moreover, ventricular rate slowing by AVN-VS provided better hemodynamic benefit than AVN ablation and right ventricular pacing. Further, it has also been demonstrated that beneficial long-term ventricular rate slowing during AF can be achieved by implantation of a nerve stimulator attached to the epicardial AVN fat pad and is an attractive alternative to other methods of rate control.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.